I have said very mean things about Victoria Beckham in my time, such as that she could neither dance nor sing and should give up her disastrous efforts at a solo career while she and David had some money left. I take none of them back. What I have lately come to realise is that what Victoria understands is clothes. She knows what to wear and she knows how to wear it. The revelation came in the form of an unforgettable pink dress.

The Moon dress by Roland Mouret that Victoria wore when she attended the press conference that welcomed her husband to LA Galaxy on July 13 2007 is a work of genius. Mouret’s designs usually begin with draping a model in fabric, in this case, 96% cotton and 4% elastane. By making two double-sided folds from nipple to neckline he constructed a bodice with oblique side seams joining extended cap-sleeves that stand proud of the shoulders, each stiffened by another small origami fold.

The front panel is divided by a half-belt that holds one edge of a folded tab into which two more folds are set. Some claim that the back zipper extends from nape to hem, which would mean that you can walk into the dress like a cupboard, but this impression appears mistaken. As Victoria would tell you herself, it is the extra half-inch that counts, but nearly all the women who have worn the real dress have given into the temptation to wear it a size too small.

Not Victoria. As she prowled along the hot green turf of the playing field, the perfect background colour for the cold pink of the dress, the half-belt sat flat on her natural waist and the skirt moved easily. Off the peg, the Moon dress would set you back about £1,000. By teaming it with a matching pink bag by Hermes and hoisting herself five inches higher on stupendous Balenciaga heels, with no added tat, no bling, no gloves, no hat, Victoria did that clever, innovative dress proud.

On GMTV last Thursday, Kate Garraway wore a knock-off of the Mouret Moon dress. Several such knock-offs are doing the rounds; this one was a near replica and all wrong. Next to the red sofa, the pink turned puce. The dress was much too small, so small puffs of flesh extruded at each armhole. The cap sleeves were too meagre and because the dress was too tight they sat too close into the neck, overemphasising the bust. The side-view was a disaster, every bulge mercilessly outlined.

Real elegance requires not only a great dress, but a discriminating and disciplined wearer. Suddenly I was reckoning Victoria Beckham among the all-time greats, alongside Wallis Simpson and Coco Chanel.

It must have been Victoria Beckham who sold the idea of managing Mouret to Simon Fuller (pictured with the Beckhams), who parlayed the Spice Girls to their success, and has continued to manage her and David Beckham ever since.

When Mouret showed his first collection at London Fashion Week in 1998, he was the property of Sharai and Andre Meyers, who had 100% of the label. In 2005, he was named red carpet designer of the year at the British Fashion Awards.

In October 2005, Mouret (pictured with Scarlett Johansson) dissociated himself from the Meyerses, leaving them holding the name Roland Mouret Designs and nothing else, and gave himself extended sick leave. His next dress, the Titanium, was so eagerly awaited that to get one you had to put your name down, wait for months, and save up £950.

When the Mouret label was relaunched in 2007 as 19RM, in homage to Fuller’s 19 Entertainment, Mrs Beckham bought all 21 items in the collection, for a mere £30,000 or so, the price of three of her Hermes Birkin handbags (pictured right). She had probably already decided to wear the Moon dress for her appearance at LA Galaxy four months before it would be available in any department store.

Because it would be seen in sunlight and therefore in its true hue, she chose orchid pink, an unusual colour for her. Ordinary mortals could buy the dress in black, white (currently for sale on Net-a-porter) or navy; only Bergdorf Goodman in New York would ever carry the pink. In darker colours, the architecture of the dress is difficult to appreciate; in pink, every fold counted.

Victoria Beckham may have seemed the least talented of the Spice Girls but her real talent lay elsewhere. She is an artist in the same genre as Damien Hirst: marketing. In an era of bare bellies, painted legs, visible underwear, junk jewellery and grisly computer generated prints, she is a lone champion of elegance for working girls.

In an endorsement for the paperback edition of her book, That Extra Half an Inch, Mouret credits her with making “high fashion relevant for everyone”. So why does she always pout? Why doesn’t she ever smile? I reckon it’s -because she knows that when she smiles, she looks like a chipmunk. Anyway, grinning isn’t glamorous.